First, a frame structure and a resource structure of a wireless communication system will hereinafter be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating a frame structure of a wireless communication system. Referring to FIG. 1, one frame includes 10 subframes, and one subframe includes two slots. A time required to transmit one subframe is defined as a Transmission Time Interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.
One slot may include a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols. The OFDM symbol may be referred to as an SC-FDMA symbol or a symbol duration.
One slot may include 7 or 6 OFDM symbols according to a cyclic prefix (CP) length. The Long Term Evolution (LTE) system includes a normal CP and an extended CP. As to the normal CP, one slot may include 7 OFDM symbols. As to the extended CP, one slot may include 6 OFDM symbols. The extended CP is used for a high delay spread.
FIG. 2 shows a resource structure of one DL slot. Referring to FIG. 2, one slot includes 7 OFDM symbols. A resource element (RE) is a resource region including one OFDM symbol and one subcarrier. A resource block (RB) is a resource region including a plurality of OFDM symbols and a plurality of subcarriers. For example, the RB may include 7 OFDM symbols in a time domain and 12 subcarriers in a frequency domain. The number of RBs contained in one slot may be determined according to downlink bandwidth.
FIG. 3 is a diagram showing the structure of a downlink subframe.
Referring to FIG. 3, a maximum of three OFDM symbols of a front portion of a first slot within one subframe corresponds to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to a data region to which a Physical Downlink Shared Channel (PDSCH) is allocated. Examples of downlink control channels used in the LTE system include, for example, a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid automatic repeat request Indicator Channel (PHICH), etc.
The PCFICH is transmitted at a first OFDM symbol of a subframe, and includes information about the number of OFDM symbols used to transmit the control channel in the subframe. The PHICH includes a HARQ ACK/NACK signal as a response to uplink transmission. The control information transmitted through the PDCCH is referred to as Downlink Control Information (DCI). The DCI includes uplink or downlink scheduling information or an uplink transmission power control command.
The PDCCH transmits a PDSCH transmission format and PDSCH resource allocation information.
In order to extend cell coverage of a mobile communication system and to increase system throughput, multi-hop transmission has been proposed. The multi-hop transmission is a communication method using a relay. The relay is referred to as a relay station (RS), a relay node (RN), etc.
A link between a base station (BS) and a relay node (RN) is referred to as a backhaul link, and a link between a relay node (RN) and a user equipment (UE) is referred to as an access link.
With the development of the relay node (RN), there is a need to define a method for transmitting/receiving a control format indicator channel of a backhaul link.